# What 'Parametric' is All About

Hey everyone! I’ve noticed a few times now in different topics where people have mentioned how they weren’t 100% sure what parametric meant. Personally, I’ve been a little obsessed with the concept in the last couple years, so I figured I’d make this thread as a place to let everyone discuss what this whole ‘parametric’ buzzword is all about.

So, what does parametric mean? In the simplest terms, something parametric is anything with a final form controlled by a series of variables. As the variables change, so does the form.

So, rather than modelling a cube by drawing a 6" x 6" square and lofting it 6" high, you would establish rules, or parameters, saying length=x, depth=y, and height=z. That means if you decide later than you want your cube to be 8" high, rather than remodeling your form all you would have to do is go to your height parameter and change height=6" to height=8". Then, your final cube form will update itself to reflect the change. For example, here’s a link showing just how many options you can build into a parametric box builder:
https://scratch.mit.edu/projects/161249/

This parametric ability isn’t just limited to 3D forms, either! You can have scripts that will output linework, even svg. files for direct laser cutter use. Here is a website full of parametric templates for packaging:
http://www.templatemaker.nl/

Super awesome, right? Especially when you start expanding from cubes and getting into more complicated geometry. One of the more crazy examples I can think of that utilizes parametric modeling is the design firm Nervous System, who will let you control and customize the forms of their 3D printed jewelry:
https://n-e-r-v-o-u-s.com/kinematics/?t=0

Hope this thread will start to clear things up for everyone!

17 Likes

To add to this it can also be associative (questionable where this is actually “design” but it’s useful)

Example: you have a board that will have something mounted to it. The mounting holes are all different diameters. You can “tell” the script that you want to label them by size with the associated screw size. It will then generate the text to engrave and place it in a determined place (say 2 mm above the hole). Your final bored will have the hole and each hole will be labeled for each size screw you need.

Comes in handy when creating stuff for others to assemble.

1 Like

That kind of use is totally design! Or if you have a design with lots of variable interlocking pieces, part of your script can be to label all of them so that you don’t have to go through one by one and do it yourself.

There are even super crazy scripts where you can be modeling in 3D, and part of the script will output all the linework for your pieces, label them, AND add construction tabs. Outputting the linework parametrically is a huge time saver, and something I’m still trying to teach myself how to do, haha.

Well, I cannot find it now… but long ago I had seen a page discussing the value of optimizing a parametric model (I think that was the intent… been a while). It gave lovely demonstrations using a bicycle model, which you want to re-size the frame of.

If you intend to keep the same wheel size, but change the frame size, then in a system where you set the parameters properly, you just change the value of “rider height” or whatever you used to set how high the seat is, and the model will change the height at which the seat rests, without losing connections to the wheels or changing the overall appearance of the cycle.

But, without parametric controls at all, you must manually adjust the size of each of a few dozen individual components, and re-attach each one as you go.

If you had things flagged as attached, but their sizes were all manual entry, then as you change the size of each one, your entire bike contorts into unimaginable shapes, or breaks the model completely when things just cannot possibly remain attached on both ends anymore.

With parametric controls applied too strictly (absolutely everything ties to a single variable, or something equally silly), you return to one of the “didn’t even parameterize” conditions, because trying to change the seat height will change the wheel size as well (and while it is nice and easy to get rods of different lengths for the frame, getting a custom sized tube is just not worth it)

Really wishing I could find the example page. It is likely far better than my attempt to describe it, at the least for having pictures. With luck, someone else knows what I am talking about and can find it.

3 Likes

I know of a grasshopper script for rhino which takes a 3D model, slices it (contour) and then lays them on a flat material so they are not intersecting and outputs as a AI file(I think). It was super useful. I’ll see if I can find it.

2 Likes

That’s a great example! In architecture, we run into the same kind of constraints in terms of knowing what and how much to make parametric.

Ooooh, yes, gimme all the grasshopper scripts! Haha love it, I had a similar script in school for making topo maps for my site studies, but it was a little clunky.

http://lmnarchitects.com/tech-studio/fabrication/contour-tool/ Heres the write up.

At the bottom of the page you can download the component. Ive never used it but you should try it and post results … I don’t have rhino anymore

Also @steph_ What kind of architecture do you do? Im a Landscape Architect (in training). Parametric design is becoming HUGE in architecture. I have some friends in Architecture and they start learning programming day one.

3 Likes

Awesome, thanks!! I’m giving myself a nice, long two-week break from work starting this Friday- perfect time to do some Rhino-ing!

I majored in architectural design at school, and now I’m at a firm in DC that does pretty much everything but prisons or hospitals. Landscape, nice! We had a landscaping course all about utilizing parametrics and computation in land formations- some awesome stuff came out of that studio. Parametric design went crazy at school, especially during my last two years there. A little too crazy, in my opinion- sort of turned into “dude look at this crazy looking thing I made in grasshopper!”

Aw man, your architect friends got to learn programming? So jealous! If you wanted to use grasshopper at my school you basically had to teach yourself- and forget about python or any other scripting language lol.

1 Like

We run into that problem with sizing prosthetic hands (e-NABLE). The finger “bones” are connected using pins through holes and cording or elastic is run through channels in the fingers & hand/palm section. Every recipient needs a different sized prosthetic so we start with a reference size and then scale it up or down to get the size needed. The trouble with standard modeling is the pins or channels & the pin holes size disproportionately to each other relative to the hand and the resulting 3D printed parts are either a bit tight or loose & some need to be tweaked & reprinted.

A parametric hand design allows us to resize based on the width and length of the recipient’s vestigial palm (our designs require at least the stump of a “hand” with a bendable wrist. Using those measurements every piece of the prosthetic can then get sized appropriately. The aesthetics are better too - every part doesn’t scale linearly just like in real life. If my fingers are 50% longer than someone else’s they’re not likely to be 50% wider or thicker, maybe only 20% thicker (long slim fingers). Humans scale non-linearly so a parametric model lets the maker get just the right size dialed in before firing off a 12 hour print.

8 Likes

I use parametrics in cabinetry all the time. For our cnc programs, I have a bunch of if statements that change how many shelves are created per cabinet based on if the type requires shelves, amount per size, and adjusts depth and length accordingly. So for every 30cm of opening , one more shelf is added. And that’s only a small part of it. Base cabinets can have full gables or recessed, maybe only on one side. Hole patterns for undermount vs Blum metal box slides. And so much more. Never mind just resizing the same box over and over.

And depending on programs, you can import variables from other programs. For Biesse machines , they can read csv files, which are basically formatted text files. I have an excel spread sheet that i just type the box type and size and a few options, save as csv, then import into the nesting software. Excluding specialty boxes, I rarely have program stuff.

It’s easy to be intimidated by parametrics at first. I need 4000 variables , and 3000 of them require dependancy on the first 1000 . And you freak out and don’t know where to start. I found that the easiest way to go at it is to build your very basic , base case scenario , no parametrics. Then tinker with it one thing at a time. Start with your major resizing first, length, width , depth, then build the rest over time. And by time I mean maybe months of tinkering as you get comfortable. It is just a computer program, save before every change, save many versions, and if you truly screw up, it’s just 1s and 0s. The real material is still in the shop, unscathed.

Parametrics is the move from pretty lines on a page that make pretty pictures , to intelligent design. Where AutoCAD gives a pretty picture that you have to interpret , to something like solidworks, where your thing is almost a real thing.

2 Likes

Just recently I have learned the real meaning of parametric, the word gets bounced around a lot and is misused a lot but when I started using Fusion 360 it all became clear. Not sure how thick the plywood you are using is going to be? Just enter your closest guess and name it plythickness. Punch in "plythickness everywhere you need it and when you take set of calipers to your plywood and it is .245 instead of .25 you just update your database and instantly everything that depends on how thick the plywood is adjusts. It is pure greatness!

1 Like

I use that for cabinetry as well. Sometime the material is 18.5 mm or 19.1. So a cabinet bottom isn’t 600 mm, its overall width minus (2x material thickness).

1 Like

You work at e-NABLE? That’s so awesome!! The work they do is amazing and inspiring

1 Like

@steph_: Yep. e-NABLE is doing some great stuff. It’s a really good example of what some of the new technologies can do when paired with new delivery models - very few of the thousands of volunteers ever meet each other face-to-face, we’re all virtual which is in itself something of a new organizational model. As a hobbyist & tech guy who doesn’t need 3D printing for my business, having it be able to be used for more than making interesting & useful little things in the garage is a great way to show some of the potential of these technologies as well as being able to do something for someone to fundamentally change their lives. Kids, especially in 3rd world and war ravaged countries, don’t usually get prosthetics because they outgrow them so quickly. But having one is hugely impactful - there’s a big difference between being able to hold an item like they can when they hold it pressed between their body and their arm and when they can manipulate it by being able to grasp it with their prosthetic. They can swing a bat, ride a bike and do other things that require grasping/holding away from the body and manipulating with their whole hand. It keeps the 3D printer from being nothing more than a 1st world privileged toy.

I’m looking forward to the GF to see if we can do something that helps complement that effort or if there are other problems like that which can be solved using this technology that aren’t being addressed now.

8 Likes

x1,000 like everything you said. I got to visit e-NABLE’s booth at the New York Maker Faire, and every kid who was there loved it! Can’t wait to see how you guys incorporate tools like the glowforge

1 Like

Which day were you there? I was down there myself on Sunday helping man the booth We had tons of folks stop by & see what could be done. Some new volunteers and a bunch of schools looking to get involved.

2 Likes

Haha no way, really? I bet we passed right by! I was there on Sunday morning-ish; I talked for a bit with someone about the potential for making a prosthetic finger for my uncle.

This thread is really fascinating and shows me just how much there is that I don’t have a clue about; but I really want to. I’ve heard of e-NABLE and I love the work you are doing with the prosthetic hands. That-more than anything- makes me want a 3D printer. I don’t know that I plan to be an architect of landscaping or buildings; but I understand what you are discussing from experience laying out and building a deck, a wall… very basic and very analog stuff. How does a person with zero background, out of college 15 years ago, learn this stuff? Where should I start? I went to the links that @steph_ posted beginning this thread, and I couldn’t figure out where to begin with the 3D cube. I lack the base knowledge for your recommended beginning.

1 Like

No worries @merindareeder Thats why were here, to help!

Do you have 3D modeling experience? Not that you need it, it will just help me answer you better